V. Bosacek, FORMATION OF SURFACE-BONDED METHOXY GROUPS IN THE SORPTION OF METHANOL AND METHYL-IODIDE ON ZEOLITES STUDIED BY C-13 MAS NMR-SPECTROSCOPY, Journal of physical chemistry, 97(41), 1993, pp. 10732-10737
Methanol and methyl iodide as methylating agents react chemically with
the surface atoms of zeolites and, under favorable conditions, yield
surface-bonded methoxy groups. Zeolites with well-defined structures o
f faujasites, mordenites and ZSM5-containing various cations (Na+, Rb, Mg2+, Ca2+) and/or acid protons were investigated in chemisorption e
xperiments using CH3I. The observed signals in the 53-59 ppm TMS regio
n were assigned to the methoxy groups, i.e., methyl groups surface-bon
ded to the lattice oxygens. The chemical shift of these signals depend
s linearly on the equalized electronegativity of the oxygen of the giv
en zeolite structure and becomes a measure of the lattice oxygen basic
ity (nucleophility). A new method has been proposed for basicity (nucl
eophility) detection of different lattice oxygens in zeolites, based o
n the C-13 MAS NMR signals of surface methoxyls in high magnetic field
experiments.